1. Field of the Invention
The present invention relates to cryogenic, high resolution, high count-rate X-ray detectors constructed of Superconducting Tunnel Junctions (STJs). The STJ detectors described herein may prove useful in microanalysis, synchrotron X-ray florescence (XRF) applications, and XRF analysis of light elements (such as Be, B, C, N, O, and F, using K lines), and transition elements (using L lines).
2. Description of Related Art
Cryogenic detectors have been under development as energy dispersive X-ray detectors with high energy resolution for the past ten years. While the energy resolution for X-rays achieved with some cryogenic detectors is an order of magnitude better than for conventional, ionization-based semiconductor detectors, most of the cryogenic detectors developed so far suffer from slow speed. Faster cryogenic detectors developed by others did not exhibit good energy resolution.
Other cryogenic X-ray detectors with good energy resolution require cooling far below the 500 mK required of this device, and additionally require thermal stabilization.
Traditional ionization-based semiconductor detectors, while operable at room temperature, provide only significantly worse energy resolution for soft X-rays.
The invention involves a sequence of thin film layers built up on a substrate.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings.
The present invention is a cryogenic, high-resolution X-ray detector with high count rate capability. The new X-ray detector is based on superconducting tunnel junctions (STJs), and operates without thermal stabilization at or below 500 mK. The X-ray detector exhibits good resolution (xcx9c5-20 eV FWHM) for soft X-rays in the keV region, and is capable of counting at count rates of more than 20,000 counts per second (cps). Simple, FET-based charge pre-amplifiers, current pre-amplifiers, together with conventional spectroscopy shaping amplifiers can provide the electronic readout of this X-ray detector.
The feasibility of operating a STJ detector cooled to below 500 mK in the environment of a room-temperature synchrotron beam line has been demonstrated. The results indicate that STJ detectors may prove very useful in X-ray fluorescence measurements and microanalysis applications studying light elements and transition metals with X-ray lines in the region below 1 keV. With the measured STJ detector resolution, the K X-ray lines from the low-Z elements such as Be, B, C, N, O, and F and possibly transition element L lines in between can easily be resolved. In this region the energy resolution of conventional semiconductor detectors, such as Si(Li) detectors, is about an order of magnitude worse than the resolution provided by an STJ detector and not sufficient to separate most of the low-Z element K lines and transition metal L lines.